Chunming Tu

Development of Hybrid Active Power Filter Based on the Adaptive Fuzzy Dividing Frequency-Control Method

This paper deals with a hybrid active power filter with injection circuit (IHAPF). It shows great promise in reducing harmonics and improving the power factor with a relatively low capacity active power filter. This paper concluded that the stability of the IHAPF based on detection supply current is superior to that of others. To minimize the capacity of IHAPF, an adaptive fuzzy dividing frequency-control method is proposed by analyzing the bode diagram, which consists of two control units: a generalized integrator control unit and fuzzy adjustor unit. The generalized integrator is used for dividing frequency integral control, while fuzzy arithmetic is used for adjusting proportional-integral coefficients timely. And the control method is generally useful and applicable to any other active filters. Compared to other IHAPF control methods, the adaptive fuzzy dividing frequency control shows the advantages of shorter response time and higher control precision. It is implemented in an IHAPF with a 100-kVA APF installed in a copper mill in Northern China. The simulation and experimental results show that the new control method is not only easy to be calculated and implemented, but also very effective in reducing harmonics.

An Improved Reactive Current Detection and Power Control Method for Single-Phase Photovoltaic Grid-Connected DG System

In the single-phase photovoltaic (PV) grid-connected distributed generation (DG) system located at the end of the feeder, it is necessary to provide quickly active and reactive power to the local loads. In this paper, an improved reactive current detection and power control method are proposed to realize active power control and reactive power compensation. To detect quickly the loads reactive current, a fast reactive current detection method using the derivative and ip-iq algorithm is presented, and it can overcome the long delay in a conventional phase-shift method. In the inner current loop, the quasi-proportional-resonant (QPR) control method with grid voltage feed-forward is presented to control accurately the grid current with zero steady error, and to reduce the current distortion due to the frequency offset and distortion of the grid voltage. The inner loop stability is analyzed, and the proper parameters are selected. In the outer loop, proportional-integrator (PI) controller is applied to stabilize the dc-link voltage, and power feed-forward is introduced to speed up system response. Simulation and experimental results verified the validity of the proposed control method.

Series and Parallel Resonance Problem of Wideband Frequency Harmonic and Its Elimination Strategy

The extensive use of pulse width modulation control technology in smart grid will lead to prominent enlargement of high-frequency harmonics. The effects of the distributed capacitances of transmission line and transformer that are neglected previously will be very obvious. The performance of the traditional harmonic eliminating method for wideband harmonic is limited, which will lead to huge challenge to the analysis, evaluation, and elimination of harmonics as well as series and parallel resonance problem. In this paper, to accurately describe the influence of wideband harmonic on smart grid, the multiterminal analysis model of harmonic degradation in smart grid is established, especially the distributed capacitances of the transmission line and the transformer are considered. Then, a novel topology of hybrid active power filter (HAPF) for resonance damping and multitype harmonic eliminating is proposed. The resonance damping model of the new topology is established; analysis results indicate that the proposed HAPF has a good harmonic resonance damping characteristic. Both simulation and experimental results have validated the validity of the theoretical analysis in this paper.

A Railway Traction Power Conditioner Using Modular Multilevel Converter and Its Control Strategy for High-Speed Railway System

With the development of high-speed and high-power electrified railway, power quality of traction power grid becomes more serious. In order to achieve three-phase balance of traction power grid, a modular multilevel converter (MMC)-based railway traction power conditioner (RTPC) is studied, which is characterized by modular multilevel cascaded structure. The RTPC consists of four H-Bridge links and output filter inductors, which can be connected to 27.5-kV traction feeders in co-phase supply system directly. This conditioner can be used for different kinds of traction system, especially suited to Scott traction system. According to the analysis of equivalent electrical model and power balance of RTPC, a hierarchical control strategy is put forward aiming to balance the submodule capacitor voltages, which ensures the safety and stability of system. Finally, the structure and its control strategy are verified by the simulation and experiment effectively.

Rapid reactive power control method for parallel inverters using resistive-capacitive output impedance

For parallel multi-inverters, an inverter using resistive-capacitive output impedance (RC-inverter) is proposed. The equivalent output impedances of RC-inverter are designed as resistive-capacitance by introducing virtual resistive-capacitive impedance into the feedback of output current. RC-inverters can not only provide rapid reactive power for low-voltage microgrid to maintain the system voltage stability, but also restrain high frequency resonance between output impedance of inverters and the grid impedance. Based on the equivalent modeling of RC-inverter, a multi-loop power sharing control method for parallel inverters is presented, which mainly includes the outer power droop control, the virtual impedance, and the output voltage control. The simulation and experimental results verify the validity of the proposed control method.

A deadbeat control method for circulating current between parallel-connected inverters

Circulating current restraining is the key technology for the reliable operation of parallel-connected inverters. This paper proposes a deadbeat zero-sequence circulating current control method based on the compensation principle of zero-sequence voltage difference, which is presented for the parallel operation of redundant grid-connected inverters with common dc bus in microgrid. Firstly, the equivalent circuit model of circulating current between parallel inverters is analyzed, the compensation quantity of zero-sequence voltage difference between inverters is obtained by the deadbeat current control method according to the zero-sequence current feedback of a single inverter and. Then, the zero-sequence voltage difference between parallel inverters is close to zero for restraining the zero-sequence current by adjusting the zero-sequence voltage of a single inverter. Finally, simulation and experiment results verified the validity of the proposed control method for zero-sequence circulating current between parallel inverters.

Key Application Technologies of High Efficiency Power Quality Control Systems

Large capacity reactive power compensation and harmonic control in the low-voltage grid of an enterprise, are important technical means to improve power quality and reduce power loss. In this paper, the principle of an efficient power quality controller is analyzed. Then, key application technologies of the HPQC which would influence the performances of the HPQC are studied. Based on an analysis of the harmonic shunt problem, a frequency dividing control strategy of the HPQC continuous subsystem is proposed. A parameter design method of the HPQC discrete subsystem and its installation method are also proposed to ensure the system compensation effect. HPQC systems have been designed for a copper foil plant. The effectiveness of this paper has been verified by the simulation and application results.